Re: kernel BUG at fs/btrfs/relocation.c:437!

[Johannes Rohr <jorohr@gmail.com>]

Sorry for nagging, but since I got no replies and neither found any
other reports that refer to line 437 of fs/btrfs/relocation.c I thought
I should ask again.

This is about a system running Ubuntu 20.04, uname -a says:

Linux ida.rooot.de 5.4.0-45-generic #49-Ubuntu SMP Wed Aug 26 13:38:52
UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

That's a kernel package that was released 31 Aug.

I can reproduce the bug by running btrfs balance start /home -musage=70

After a few seconds, the command terminates with a segfault, dmesg
output is here:
https://gist.github.com/vasyugan/340d9cd2292e3122c1d7773df718a234

The core lines in dmesg seem to be:

[32387.616248] ------------[ cut here ]------------

[32387.616249] kernel BUG at fs/btrfs/relocation.c:437!

[32387.616271] invalid opcode: 0000 [#1] SMP PTI
[32387.616180] BTRFS error (device sdc2): couldn't find block
(4853431877632) (level 1) in tree (19918) with key (986 96 124)


There is nothing about an IO error in dmesg, so to me as a layman this
doesn't look like physical damage.

Yet when I repeat the command, it always names the same block.

I have of course run scrub, which as I understand it, does the same that
an  offline btrfs check  would do, it finds no errors.

It would be awesome if anyone could take this up.

I have submitted the bug to bugzilla:
https://bugzilla.kernel.org/show_bug.cgi?id=209143

Cheers,

Johannes


Am 01.09.20 um 10:18 schrieb Johannes Rohr:
> Dear devs,
>
> I tried to replace an SSD with bad S.M.A.R.T. status and since I don't
> have physical access to the server, I first wanted to remove it from the
> RAID 1 (which has 4 SSDs) and then erase it.
>
> I ran "btrfs device delete /dev/sda2 /". After a while, the command
> terminated with a segfault and the system hung. I waited for 30 minutes.
> Fortunately, it could be resurrected with a hard reset.
>
> dmesg, as this happened, reports that a block on a different SSD, on
> /dev/sdc can't be found.
>
> See full backtrace here:
> https://gist.github.com/vasyugan/340d9cd2292e3122c1d7773df718a234
>
> Now I am afraid that if sda is just removed physically, then marked as
> degraded and swapped for a new SSD using the btrfs replace command, this
> might also go bad  because of the block that can't be found.
>
> Does any of you have advice on what to do? From the backtrace I don't
> even understand if the issue is a physical problem with sdc (whose
> S.M.A.R.T. values are just fine) or whether this is another btrfs bug
> and if you, if there is any way to work around it.
>
> We are running Ubuntu 20.04, the kernel is 5.4.0-45-generic, Ubuntu's
> version number is: 5.4.0-45.49. It was released yesterday and was
> supposed to have a relocation relate bug fixed, see
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1889669
>
> I suppose, this is a separate issue. Should I report a bug? If so, where?
>
> Thanks a lot in advance for your support!!!
>
> Johannes
>
>
>